1. Field of the Invention
This invention relates generally to a chair having a backrest with a changeable support surface and especially to adjustable contour backrest.
In particular, this invention concerns a backrest for providing support to the lower back region of a chair occupant.
2. Background Art
Current seating designs for office furniture, such as task chairs, commonly incorporate multiple positional features for user comfort. With regard to backrest designs, various concepts have been utilized to support the natural curve of the spine and to relieve stress on the lumbar vertebrae.
Typical of such designs are chairs having an inflatable air lumbar support mechanism for increasing and/or decreasing the convexity of a backrest as illustrated in U.S. Pat. No. 5,660,438. A chair having a mechanically operable camming device for imparting a curvature to a backrest is disclosed in U.S. Pat. No. 3,948,558. The backrest of the chair shown in U.S. Pat. No. 4,601,514 relies upon a spring member for varying the curvature.
A limitation of the above-described backrests is that each is primarily concerned with curvature variations in the backrest without compensation for the differences in location of the lumbar region of respective chair occupants.
The backrest disclosed in U.S. Pat. No. 3,642,319 utilizes a shaft having an eccentric rotary axis for modifying the convexity of and for positionally relocating the contour. A disadvantage of this mechanism is that it cannot be readily operated by a chair occupant while seated in the chair.
Additional backrest designs for positionally adjusting a lumbar support are respectively shown in U.S. Pat. Nos. 5,217,278 and 4,156,544. These backrest devices employ complex control mechanisms and are intended for use in vehicle seats rather than for office furniture.
The backrest of the present invention in contrast to the previously described devices provides a relatively simple construction and has a plurality of contour elevational settings.